3,868 research outputs found
Lyotropic Liquid Crystals From Lecithin, Water, And Polyethylene Glycol
Lyotropic liquid crystals with lecithin as the amphiphile and with water/polyethylene glycol (PEG) solutions as the solvent were prepared with polyethylene glycol/water ratios from 182 to 0. The liquid crystals were lamellar and the interlayer spacing was independent of the solvent content for water/PEG ratios ≤1 but increased strongly with the water/PEG ratio. Higher ratios gave increased interlayer spacing with solvent content similar to the variation for liquid crystals with water as solvent but the absolute values of the spacing were higher. © 1984 Academic Press, Inc. All rights reserved
A substitute for the singular Green kernel in the Newtonian potential of celestial bodies
The "point mass singularity" inherent in Newton's law for gravitation
represents a major difficulty in accurately determining the potential and
forces inside continuous bodies. Here we report a simple and efficient
analytical method to bypass the singular Green kernel 1/|r-r'| inside the
source without altering the nature of the interaction. We build an equivalent
kernel made up of a "cool kernel", which is fully regular (and contains the
long-range -GM/r asymptotic behavior), and the gradient of a "hyperkernel",
which is also regular. Compared to the initial kernel, these two components are
easily integrated over the source volume using standard numerical techniques.
The demonstration is presented for three-dimensional distributions in
cylindrical coordinates, which are well-suited to describing rotating bodies
(stars, discs, asteroids, etc.) as commonly found in the Universe. An example
of implementation is given. The case of axial symmetry is treated in detail,
and the accuracy is checked by considering an exact potential/surface density
pair corresponding to a flat circular disc. This framework provides new tools
to keep or even improve the physical realism of models and simulations of
self-gravitating systems, and represents, for some of them, a conclusive
alternative to softened gravity.Comment: Accepted for publication in A&A; 7 pages, color figure
Cosmological Simulations of Massive Compact High-z Galaxies
In order to investigate the structure and dynamics of the recently discovered
massive (M_* > 10^11 M_sun) compact z~2 galaxies, cosmological
hydrodynamical/N-body simulations of a proto-cluster region have been
undertaken. At z=2, the highest resolution simulation contains ~5800 resolved
galaxies, of which 509, 27 and 5 have M_* > 10^10 M_sun, > 10^11 M_sun and >
4x10^11 M_sun, respectively. Effective radii and characteristic stellar
densities have been determined for all galaxies. At z=2, for the definitely
well resolved mass range of M_* > 10^11 Msun, the mass-size relation is
consistent with observational findings for the most compact z~2 galaxies. The
very high velocity dispersion recently measured for a compact z~2 galaxy (~510
km/s; van Dokkum et al 2009) can be matched at about the 1-sigma level,
although a somewhat larger mass than the estimated M_* ~ 2 x 10^11 M_sun is
indicated. For the above mass range, the galaxies have an average axial ratio
= 0.64 +/- 0.02 with a dispersion of 0.1, an average rotation to 1D
velocity dispersion ratio = 0.46 +/- 0.06 with a dispersion of 0.3,
and a maximum value of v/sigma ~ 1.1. Rotation and velocity anisotropy both
contribute in flattening the compact galaxies. Some of the observed compact
galaxies appear flatter than any of the simulated galaxies. Finally, it is
found that the massive compact galaxies are strongly baryon dominated in their
inner parts, with typical dark matter mass fractions of order only 20% inside
of r=2R_eff.Comment: 10 pages, 8 figures, submitted to Ap
Effect of dark matter halo substructures on galaxy rotation curves
The effect of halo substructures on galaxy rotation curves is investigated in
this paper using a simple model of dark matter clustering. A dark matter halo
density profile is developed based only on the scale free nature of clustering
that leads to a statistically self-similar distribution of the substructures at
galactic scale. Semi-analytical method is used to derive rotation curves for
such a clumpy dark matter density profile. It is found that the halo
substructures significantly affect the galaxy velocity field. Based on the
fractal geometry of the halo, this self-consistent model predicts an NFW-like
rotation curve and a scale free power spectrum of the rotation velocity
fluctuations.Comment: 6 pages, 3 figures. Accepted for publication in ApJ. The definitive
version will be available at http://iopscience.iop.org
The Structure Of Lamellar Lyotropic Liquid Crystals From Lecithin And Alkanediols
Lamellar liquid crystals from lecithin and alkane diols were studied to determine the composition range of stability and geometrical dimensions using low-angle X-ray scattering. An estimation of the dislocation pattern was made from the optical pattern in polarized light. The ethylene glycol gave the widest range of stability for the lamellar structure, the range being reduced toward heptane diol, the longest member to give liquid crystals. The interlayer spacing was reduced with increasing chain length of the diol and the dislocation pattern remained identical. © 1981
Dissecting Galaxy Formation: II. Comparing Substructure in Pure Dark Matter and Baryonic Models
We compare the substructure evolution in pure dark matter (DM) halos with
those in the presence of baryons (PDM and BDM). The prime halos have been
analyzed by Romano-Diaz et al (2009). Models have been evolved from identical
initial conditions using Constrained Realizations, including star formation and
feedback. A comprehensive catalog of subhalos has been compiled and properties
of subhalos analyzed in the mass range of 10^8 Mo - 10^11 Mo. We find that
subhalo mass functions are consistent with a single power law, M_sbh^{alpha},
but detect a nonnegligible shift between these functions, alpha -0.86 for the
PDM, and -0.98 for the BDM. Overall, alpha const. in time with variations of
+-15%. Second, we find that the radial mass distribution of subhalos can be
approximated by a power law, R^{gamma} with a steepening around the radius of a
maximal circular velocity, Rvmax, in the prime halos. Gamma ~-1.5 for the PDM
and -1 for the BDM, inside Rvmax, and is steeper outside. We detect little
spatial bias between the subhalo populations and the DM of the main halos. The
subhalo population exhibits much less triaxiality with baryons, in tandem with
the prime halo. Finally, we find that, counter-intuitively, the BDM population
is depleted at a faster rate than the PDM one within the central 30kpc of the
prime. Although the baryons provide a substantial glue to the subhalos, the
main halos exhibit the same trend. This assures a more efficient tidal
disruption of the BDM subhalos. This effect can be reversed for a more
efficient feedback from stellar evolution and supermassive black holes, which
will expel baryons from the center and decrease the concentration of the prime
halo. We compare our results with via Lactea and Aquarius simulations and other
published results.Comment: 12 pages, 9 figures, to be published by the Astrophysical Journa
Coronary artery disease-associated genetic variants and biomarkers of inflammation
Introduction: Genetic constitution and inflammation both contribute to development of coronary artery disease (CAD). Several CAD-associated single-nucleotide polymorphisms (SNPs) have recently been identified, but their functions are largely unknown. We investigated the associations between CAD-associated SNPs and five CAD-related inflammatory biomarkers. Methods: We genotyped 45 CAD-associated SNPs in 701 stable CAD patients in whom levels of high-sensitivity C-reactive protein (hsRCP), interleukin-6, calprotectin, fibrinogen and complement component 3 levels had previously been measured. A genetic risk score was calculated to assess the combined risk associated with all the genetic variants. A multiple linear regression model was used to assess associations between the genetic risk score, single SNPs, and the five inflammatory biomarkers. Results: The minor allele (G) (CAD risk allele) of rs2075650 (TOMM40/APOE) was associated with lower levels of high-sensitivity C-reactive protein (effect per risk allele: -0.37 mg/l [95%CI -0.56 to -0.18 mg/l]). The inflammatory markers tested showed no association with the remaining 44 SNPs or with the genetic risk score. Conclusions: In stable CAD patients, the risk allele of a common CAD-associated marker at the TOMM40/APOE locus was associated with lower hsCRP levels. No other genetic variants or the combined effect of all variants were associated with the five inflammatory biomarkers
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